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Full text of "The North American forms of Lasius umbratus Nylander."

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tfi. Brown, Jr. 


[Reprinted from PSYCHE, Vol. XVII, No. 6, 1910.] 



Like many other ants that are peculiar to the' north temperate 
zone, Lasius umbratus is very widely distributed and presents a 
number of local subspecies and varieties. In the Old World it 
ranges from England to Japan, through northern and central 
Eurasia; in North America from Nova Scotia and the Atlantic 
States to the Rocky Mountains and will probably be found on the 
Pacific Coast, at least in the mountains of California or at lower 
elevations in Washington and Oregon. According to Forel and 
Emery the species is represented in Europe by four subspecies, 
namely, the typical umbratus Nyl., mixtus Nyl., affinis Schenk and 
bicornis Forster. To these Ruzsky has added a fifth, exacutus, from 
Oriental Russia. To judge from a female specimen in my collection, 
the Japanese form is indistinguishable from the typical umbratus. 
Transitional forms which Forel has called mixto-umbratus occur in 
Switzerland, and others which Ruzsky has called umbrato-affinis 
have been taken in eastern Russia. Mayr cited three forms from 
the United States: mixtus, affinis and bicornis, but Emery has 
shown that the first of these differs slightly from the European 
mixtus and had been previously described by Walsh as Formica 
aphidicola, and that the last is a distinct subspecies which he has 
called minutus. He was unable to find affinis among his American 
material and I have been equally unsuccessful. This form, there- 
fore, is probably not represented on our continent. More recently 

'Contributions from the Entomological Laboratory of the Bussey Institution, Harvard 
University, No. 30. 

236 Psyche [December 

Viereck has described from New Mexico a new subspecies as 
subumbratus, and another subspecies, vestitus, from Idaho, is' 
added in the present paper. This form may prove to be the 
hitherto unknown female of Emery's L. speculiventris, which, I 
believe, is merely a subspecies of umbratus. 

All the various forms that constitute the species umbratus may 
be readily distinguished in the worker and female phases from 
the other species of Lasius, by the following peculiarities: the 
maxillary palpi are 6-jointed and this character places the species 
in the genus Lasius sensu stricto and removes it from the exclu- 
sively- North American subgenus Acanthomyops, which includes 
species with 3-jointed maxillary palpi and a strong odor like that 
of lemon verbena or oil of citronella. The joints of the maxillary 
palpi in umbratus are not long and subequal as in L. niger and 
its various forms, but grow successively shorter towards the tip. 
It differs from our two other Lasii with yellow workers and dimin- 
ishing maxillary joints (Z. flams nearcticus Wheeler and L. brev- 
icbrnis Emery) in having the antennal scapes extending a consid- 
erable distance beyond the posterior corners of the head, the 
larger size of the eyes in the worker, and in being more or less 
tinged with brown in this phase. Moreover, the female umbratus 
has the head as broad as the thorax, whereas in nearcticus and 
brevicornis it is distinctly narrower. It is by no means easy to 
separate the various subspecies or races of umbratus on morpholog- 
ical characters, such as the size of the eyes of the worker, shape of 
the petiole of the worker and female, dentition of the mandibles 
of the male, etc., since these characters are rather inconstant. 
More satisfactory distinctions are furnished by peculiarities of 
stature, pubescence, pilosity and color. 

Notwithstanding its wide distribution L. umbratus is by no 
means as common as other species of the genus. In North America 
however, it is much more frequently met with than in Eurasia; 
but even in our country it is sporadic, being abundant in certain 
localities and totally lacking in others. It prefers rather damp, 
shady spots like those occupied by L. nearcticus and the species of 
Acanthomyops. Like the species of this sub-genus it forms populous 
colonies under stones, in rotten stumps or logs or constructs large 
masonry dome nests. These dome nests I have seen only in 
meadows or in clearings in the woods where the soil is covered 

1910] Wheeler North American Forms of Lasius umbratus 237 

with grass and, is more or less exposed to the sun. The subspecies 
subumbratus is an exclusively boreal form, occurring only in Brit- 
ish America and at elevations above 7,500 ft. in the Rocky 
Mountains. The same is probably true of vestitus. The sub- 
species minutus and speculiventris and the variety aphidicola occur 
in the transition zone and of these only aphidicola is at all common. 
Like our other yellow Lasii, umbratus is subterranean in its habits 
and devotes itself to the care of root-aphids and -coccids, all or 
nearly all of its food consisting of the sweet excreta of these 

The sexual phases are rarely found in the nests of umbratus, 
apparently because they are not retained by the parental colonies 
for days or weeks during the latter part of the summer or early 
fall but escape for their marriage flight very soon after reaching 
maturity. Recent studies in Europe indicate that the just- 
fertilized umbratus queen is unable to establish her colony inde- 
pendently after the manner of L. niger and ftavus, but becomes a 
temporary parasite on a colony of niger or of one of its subspecies 
or varieties after the manner of certain species of Formica of the 
rufa and exsecta groups. Our American umbratus forms apparently 
behave in the same manner. De Lannoy and Wasmann, moreover, 
have collected some evidence to show that umbratus is in turn the 
temporary host of the palearctic L. juliginosus. The rare or 
sporadic occurrence of umbratus on both continents certainly 
points to parasitic habits on the part of the queen and her incip- 
ient colony. 

The following tables will facilitate the identification of workers 
and females of our North American forms of umbratus: 


1. Antennal scapes and tibise with very few or no erect hairs; gaster 

with appressed pubescence 2 

Antennal scapes and tibiae with abundant erect hairs; gaster with- 
out pubescence .' subsp. speculiventris Emery. 

2. Gaster with sparse pubescence and short erect hairs,. shining; aver- 

age length of body over 4 mm 3 

Gaster very densely pubescent, with long erect hairs, subopaque; 
average length of body less than 4 mm subsp. minutus Emery. 

3. Pale yellow; eyes small subsp. subumbratus Viereck. 

Brownish yellow; eyes larger. .. .subsp. mixtus Nyl. var. aphidicola Walsh. 

238 . Pysche [December 


1. Length not exceeding 4.5 mm suljsp. minutus Emery. 

Length not less than 6 mm 2 

2. Scapes and legs covered with dense, erect hairs; length 

6 mm. subsp. vestitus subsp. nov. 

Scapes and legs naked or with only a few scattered erect hairs; 

average length more than 6 mm: 3 

3. Body dark brown above; erect hairs on the gaster very short or 

absent subsp. mixtus Nyl. var. aphidicola Walsh. 

Body light brown or reddish; hairs on gaster very long, reclin- 
ate subsp. subumbratus Viereck. 

1. Lasius umbra tus subumbratus Viereck. 

Trans. Ent. Soc. Phila. XXIX, 1902, p. 72. 9 . 

Worker. Length 4-5.5 mm. 

Very similar to the typical umbratus. Body shining and rather smooth, especially 
the clypeus and gaster. Pubescence and p ilosity abundant, the former more so on 
the head and thorax than on the gaster. Erect hairs on the- femora few and scat- 
tered, absent on the tibiae and scapes. Eyes small. Petiole high and much com- 
pressed anteroposteriorly, its sides and upper border rounded, the latter entire or 
with a very feeble notch. Pale yellow throughout, except the mandibles, which are 
reddish brown, with black teeth, and the articulations of the antennal funiculi 
wh'ch are fuscous or blackish. 

Female. Length 7-8.5 mm. 

Differing from the true umbratus as follows: Color paler, being a light brown or 
reddish, with the lower surface and the legs more yellowish. Pubescence much 
longer and more abundant. Hairs on the head, thorax and abdomen very long, 
slender and reclinate; absent on the legs and scapes. In some specimens the hairs 
on the head are short and sparse. Border of the petiole bearing a fringe of long 
hairs, its upper border much less deeply notched than in the true umbratus. Wings 
gray, with basal halves distinctly infuscated as in the other forms of the species. 

Male. Length 3.5-4.5 mm. 

Differing from the true umbratus only in its somewhat paler color and in lacking 
erect hairs on the legs and scapes. Eyes hairy as in that form and with the man- 
dibles furnished with two larger apical and several minute basal teeth. 

This subspecies was originally and rather inadequately described 
by Viereck from two females taken at Beulah, N. M. (about 8,000 
ft.), one August 17 by Dr. H. Skinner, July 27 by Prof. T. 
D. A. Cockerell. These are in the type collection of the Phila. 
Acad. Nat. Sci. In my own collection the form is represented 
from the following localities : 

1910] Wheeler North American Forms of Lasius umbratus 

New Mexico: Beulah (Cockerell; topotype), one dealated 

Colorado: Two females, one dealated, taken by P. J. Schmitt; 
one dealated female taken by myself in Cheyenne Canon (about 
8,000 ft.), near Colorado Springs; numerous workers from Wil- 
liams Canon, near Manitou (about 7,500 ft.), also captured by 

Utah: Numerous workers from Little Willow Canon (C. V. 
Chamberlin) . 

Nova Scotia: Many workers, males and winged females taken 
from five colonies by Mr. John Russell at Digby, and six dealated 
females taken at Bedford, near Halifax by Mr. William Reiff. 

Dr. P. P. Calvert and Mr. E. T. Cresson, Jr., kindly compared 
one of the female specimens from Nova Scotia with Viereck's 
type and state that the former differs from the latter only in 
being somewhat more yellowish and less reddish. I am unable 
to detect any differences even in coloration between my Rocky 
Mountain specimens and those from Nova Scotia. v 

It is interesting to note, as bearing on the probable' temporary 
parasitism of umbratus, that the six dealated queens taken by 
Mr. Reiff at Bedford, N. S., were found living in three colonies of 
the large yellowish form of Lasius niger var. neoniger Emery so 
characteristic of boreal America. 

2. Lasius umbratus mixtus Nyl. var. aphidicola Walsh. 

Formica aphidicola Walsh, Proc. Ent. Soc. Phila. 1862, p. 310, worker cf. 
Lasius aphidicola Mayr, Verh. zool.-bot. Ges. Wien, XXXVI, 1886, p. 429; 

Dalla Torre, Catalog. Hymen. VII, 1893 p. 182. 
Lasius umbratus subsp. mixtus var. aphidicola Emery, Zool. Jahrb. Abth. f. 

Syst. VII, 1893, p. 640, 641, worker 9 cf; Wheeler, Bull. Amer. Mus. Nat. 

Hist. XXI, 1905, p. 397; Occas. Papers Bost. Soc. Nat. Hist. VII, 7, 1906, p.13. 
Lasius speculiventris Wheeler, Bull. Amer. Mus. Nat. Hist. XXI, 1905, p. 397. 

Worker. Length 3.5-4.5 mm. 

Brownish yellow, with the appendages, lower portion of the body and anterior 
portion of the head paler. Surface, especially the dorsum of the gaster shining, 
owing to the short and dilute, though distinct pubescence. Hairs erect, coarse 
and rather abundant, short on the gaster, absent on the scapes and legs. Petiole 
seen from behind with rounded or subangular sides and the notch in the upper 
border variable, but. usually feeble. 

240 Psyche [December 

Female. Length 6-7 mm. 

Dark brown; mandibles, appendages, pleurae, epinotum and petiole usually 
reddish or yellowish. Basal half of wings strongly infuscated. Pilosity and pubes- 
cence similar to those of the worker but the pubescence on the gaster denser so 
that this region is much less shining than in the worker. Erect hairs on the gaster 
often absent, when developed scattered and very short except on the terminal 
segments. Eyes very hairy. Petiole from behind with rounded sides and upper 
border, the latter feebly emarginate. 

Male. Length 4-4.5 mm. 

Mandibles with two apical and no basal teeth. Body black; appendages pic- 
eous; wings colored like those of the female. Surface, especially that of the gaster, 
smooth and shining. Pilosity moderately developed, erect; absent on the scapes 
and legs; pubescence more dilute and inconspicuous than in the worker. Eyes 

I have followed Emery in regarding this subspecies as the one 
which Walsh described as Formica aphidicola, though his descrip- 
tion is very inadequate. As it is our most common form of umbra- 
tus, it is, in all probability, the one which he saw. The types came 
from Rock Island, 111. I have examined numerous specimens from 
the following localities : 

Illinois: Rockford (Wheeler); Algonquin (W. A. Nason). 

Wisconsin: Milwaukee (C. E. Brown). 

Michigan: Ann Arbor (J. Dawson). 

Maine: Elms (W. Deane). 

New Hampshire : Mt. Washington (Mrs. A. T. Slosson). 

Massachusetts: Boston (Wheeler) ; Essex County (G. B. King); 
Medford (Mus. Comp. Zool.). 

Connecticut: Colebrook (Wheeler); Westport (W. E. Brit- 
ton) . 

New York : Bronxville (Wheeler) ; Bergen Beach (G. v. Kroc- 
kow); Staten Island (W. T. Davis). 

New Jersey: Ithaca (J. C. Bradley); Fort Lee, Great Notch 
and Ramapo Mts. (Wheeler) ; Tom's River (W. T. Davis) ; Wood- 
bury (H. Viereck). 

Pennsylvania: St. Vincent (P. J. Schmitt), Philadelphia; Tin- 
icum Islands; Enola. 

North Carolina: Black Mts. (Wm. Beutenmuller) ; Raleigh 
(F. Sherman). 

Colorado: Florissant and Colorado Springs (Wheeler); Eldora, 
8,600 ft. (Mrs. W. P. Cockerell). 

.1910] Wheeler North American Forms of Lasius umbratus 241 

Emery cites aphidicola also from Caldwell, N. J., District of 
Columbia and Virginia. According to this authority, aphidicola 
is so close to the European mixtus as to be scarcely distinguish- 
able. The color of the worker of the American form is usually 
darker, and the body and wing color of the female is decidedly 
deeper. Worker forms are sometimes found with a few, scattered 
erect hairs on the antennal scapes and tibiae and therefore repre- 
sent transitions to the typical umbratus. 

3. Lasius umbratus minutus Emery. 

Lasius umbratus vat. bicornis Mayr, Verh. zool.-bot. Ges. Wien, XXXVI. 
1886, p. 430. 

Lasius umbratus subsp. minutus Emery, Zool. Jahrb. Abth. f. Syst. VII, 1893, 
p. 641, worker 9 cf ; Wheeler, Bull. Amer. Mus. Nat. Hist. XXI, 1905, 
p. 397; Occas. Papers Bost. Soc. Nat. Hist. VII, 7, 1906, p. 13. 

Worker. Length 3-3.5 mm. 

Brown, with the cheeks, clypeus, mandibles, appendages and lower surface of 
"the body more yellowish. Body so densely pubescent that its shining surface is 
obscured and appears glossy or subopaque. Hairs on the head, thorax and gaster 
abundant, erect and coarse, on the gaster longer and more conspicuous than in the 
two preceding subspecies. Scapes and legs naked; lower surfaces of the femora 
with a few scattered, erect hairs. Petiole high and narrow, with straight sides and 
a distinct notch in the apical border. 

Female. Length 4-4.5 mm. 

Dark brown; mandibles, mouthparts and appendages, except the middle por- 
tions of the femora, pale brown; wings gray with infuscated bases. Pubescence 
and pilosity very similar to those of the worker, but longer. Petiole more feebly 

Male. Length 2.6-3.5 mm. 

Black; with piceous legs and antennae. Wings colored like those of the female. 
Mandibles with two apical and no basal teeth. Pubescence and pilosity like those 
of the worker, but the former more dilute, so that the surface of the body is more 
shining. Discoidal cell of the wing often incomplete or lacking. 

The type specimens described by Emery came from New 
Jersey and Maine. I have examined specimens from the follow- 
ing states: 

New Jersey: Cotypes (T. Pergande). 

Maryland: Chestertown (E. G. Vanatta). 

Illinois: Rockford (Wheeler). 

242 Psyche [December- 

Michigan: Ann Arbor (J. Dawson). 
Connecticut: Colebrook (Wheeler). 
Massachusetts: Forest Hills, Boston (M. Tanquary); Med- 

ford (Dall.). 

Emery has called attention to the resemblance of this species, 
which is characterized by the small size of the females and the 
peculiar pubescence and pilosity of these and the workers, to the- 
European bicornis and affinis. The description given above is 
drawn from numerous specimens of all three phases taken August 
12, 1910, taken by Mr. M. Tanquary from a large masonry dome 
nest in low ground near Forest Hills, Mass. The dealated females 
bear a remarkable resemblance in size and coloration to the cor- 
responding phase of our common Tapinoma sessile. 

4. Lasius umbratus vestitus subsp. nov. 

Female. Length about 6 mm. 

Differing from subumbratus and aphidicola in its smaller size and in pilosity. 
Body dark brown above, with paler lower surface, mandibles, antennae and legs. 
Surface finely shagreened and shining but appearing more opaque on account of 
the dense layer of fine grayish pubescence. Hairs sordid white, fine and uniformly 
abundant, erect, long on the body, shorter on the scapes and legs. The petiole, 
which is fringed with long hairs, has a peculiar shape, being in profile cuneate 
and inclined forward and rather thick at the base; seen from behind it is narrowed 
above, with a blunter and more rounded margin than in the other subspecies, and 
without emargination. Wings very long (8 mm.), faintly infuscated at the base. 

Described from a single specimen taken by Prof. J. M. Aldrich 
at Moscow, Idaho. 

This may be the female of L. speculiventris, of which Emery 
described only the male and worker. 

5. Lasius umbratus speculiventris Emery. 

L. speculiventris Emery, Zool. Jahrb. Abth. f. Syst. VII, 1893, worker cf. 

" Worker. Yellow; head subpubescent, densely hairy; scapes and tibiae hirsute 
with erect hairs; head, thorax and legs pubescent, gaster without appressed pubes- 
cence, delicately, microscopically, transversely rugulose, very shining. Length 
3.5-4 mm. 

Male. Fuscous; legs, antenna? and genitalia pale; densely pilose; scapes with 
short hairs; tibiae with scattered, scapes with short hairs; wings clouded with 
fuscous at the base. Length 3.5-4 mm., width of head 1.2 mm., length of scape 
0.7 mm., anterior wing 4.5 mm. 

1910] Wheeler North American Forms of Lasius wmbratus 243 

Cal.dwell, N. J., from Mr. Pergande. 

The worker is distinguished by the abundant, erect pilosity of 
the antennal scapes and tibiae and by the complete absence of 
appressed pubescence on the gaster. The latter region, owing to 
the lack of the fine punctures- connected with the pubescence, is 
:remarkably shining. With the aid of a very strong lens its surface 
is seen to present, in addition to the hair-bearing punctures, only 
.a very fine rugosity, in the form of long, transverse meshes. 
Whether this form is to be retained as an independent species or 
is to be regarded as a subspecies of umbratus, cannot be decided at 

In the male the antennal scape is densely covered with short, 
oblique hairs as on the male of the European umbratus; it is 
relatively short and when placed transversely reaches beyond 
the eye about two fifths of the length (in umbratus the trans- 
versely placed scape extends easily half its length beyond the eye) . 
The tibise bear only a few erect hairs. The general pilosity is 
more abundant and like that of the males of the true umbratus 
which I have before me." (Emery.) 

I have translated the original description because I have not 
seen specimens of speculiventris. In my "Annotated List of the 
Ants of New Jersey" I stated that I had taken this form at Fort 
Lee and Great Notch, but examination of these specimens shows 
that they are merely very shining examples of aphidicola. As 
the characters mentioned in Emery's description are scarcely of 
specific value, I believe that I am justified in placing speculiventris 
among the umbratus forms. As already stated the subspecies 
described above as vestitus may be merely the hitherto unknown 
female of Emery's form.